The invention relates to an injection molding machine and, more particularly, to an injection molding machine for processing plastics materials and other plasticisable compounds including at least partially electrically operated driving units to operate the machine.
A linear motor, which is used as the driving unit and is provided with a rotor and stator, is known for plastics material molding machines from DE-T2 37 82 817, which corresponds to EP 0 280 743 B1, and JP-A 63-1516, rotor and stator having cylindrical surfaces which are in operative connection with one another. These surfaces permit the magnetic face, which is needed for the required advancing forces, to be suitably incorporated in the drive axis. If stator windings are symmetrically disposed in accordance with DE-A 44 45 283, the relatively high bearing forces caused by the magnetism are mutually excluded. However, even there, mention is constantly made in the description of only one primary part and one secondary part, which parts co-operate accordingly with one another. If FIG. 3 there is additionally considered, it becomes apparent that the internally situated pipe is merely a carrier pipe which, just like the externally situated pipe, is neither a stator nor a rotor. When such a linear motor is used, there is a simultaneous saving in the complex converting means, which are susceptible to wear and serve to convert a rotary movement into a linear movement, such as, for example, a transmission mechanism, a spindle, levers and toothed rods (cf also EP-A 744 815), but the forces, which are required for a plastics material injection molding machine, cannot yet be applied,therefore to a sufficient extent.
Electrical driving units are also often used in conjunction with injection molding machines. thus, for example, it is known from EP 0 662 382 to stack together various hollow-shaft motors inside the injection molding unit to inject the plasticised compound into the injection mould and to fit the nozzle onto the injection mould. However, it is necessary for such purpose, and time-consuming, to convert the rotary movements, produced by the hollow-shaft motors, into translatory movements. However, since all of the shafts or axis for the injection molding machine are translatory shafts with the exception of the feed screw for metering the material to be plasticised, the use of such hollow-shaft motors is only recommended to a limited extent.
From handling techniques and medical techniques, linear motors are known which, however, do not have sufficient advancing forces, so that the linear motors, which are mainly fitted in a flat manner, are not suitable for use in an injection molding machine. (Company brochure entitled xe2x80x9cNew linear Motors and its applicationsxe2x80x9d produced by the company called Fanuc, published in FANUC Tech. Rev. 112, pp. 25-36 (December, 1998); specification sheet linear motors entitled Lin.Mot P belonging to Sulzer Electronics AG, Zurich.)
The present invention provides a linear motor for an injection molding machine, which motor can also apply the advancing forces required for an injection molding machine.
An injection molding machine for processing plastics materials and plasticisable materials of the present invention includes an injection molding unit and a mould closing unit, which are operated at least partially by an electric driving unit including at least one linear motor, which has a rotor with magnets, disposed along a first cylindrical surface, and a stator with stator windings disposed along a second cylindrical surface, the first and second cylindrical surfaces of stator and rotor being concentrically disposed, and the stator windings being substantially symmetrical relative to an axis of movement of the linear motor. Additionally, a plurality of identically acting first surfaces are stacked with a corresponding number of identically acting second surfaces, the first and/or second surfaces each being operable jointly in operative connection.
In consequence, various cylindrical faces can be stacked one inside the other so that a plurality of identically acting magnetic faces are produced which contribute towards increasing the advancing forces up to a range which is required for plastics material injection molding machines, e.g. for applying the closing force. The alleged disadvantage is tolerated in such case, i.e. that the linear motor can tilt more easily so that greater demands for precision are to be made on the means for guiding the parts of the linear motor. However, this is compensated for again by the more compact construction which can be achieved.
Although it is known, in prior art, which forces are required for an injection molding machine to produce molded parts, only circular arrangements were proposed there, the rotor and stator having concentric surfaces, since the person skilled in the art has probably concluded therefrom, incorrectly, that a corresponding alternative arrangement cannot be achieved to a suitable extent. In order to operate the surfaces jointly in operative connection with one another in fact, said surfaces have to be worked with appropriate precision. In such case, the precision required for the operation of the linear motor increases exponentially with an increasing spacing from the central line of the cylindrical surfaces so that the linear motor can tilt more easily, the greater this spacing is, more especially when the linear motor is to be kept short in order to achieve as compact a construction of the entire injection molding machine as possible. This is further emphasized by the high temperatures which occur at high forces. This may probably also be the reason why, despite their advantages, linear motors have not yet been successful in the field of plastics material injection molding machines, since hitherto the corresponding forces could still not be applied.
Cooling ducts may be disposed in the cylindrical walls of the stator, so that the heating, caused by the current, can be reliably dissipated. The cooling medium used therefor can, at the same time, be used to control the temperature of other component parts in the injection molding machine.